1. Field of the Invention
The present invention relates to a sheet folding device performing folding processing on a sheet where an image is formed by an image forming apparatus, such as a copier, a printer, a facsimile, or the like, and a paper post-processing device provided therewith.
2. Description of Related Art
Conventionally, a sheet folding device has been used which carries therein a sheet where an image is formed by an image forming apparatus and then performs processing of folding the sheet (a bundle of sheets), such as middle folding processing or the like. For example, the sheet folding device is built in a paper post-processing device which is provided adjacently to the image forming apparatus and which performs processing, such as punching processing for forming a punched hole at a predetermined position on a sheet and stapling processing on a plurality of sheets stacked.
More specifically, the sheet folding device includes: a receiving member for receiving a sheet carried in; a width adjusting member for correcting skew of a sheet carried in and adjusting the sheet in the width direction (direction perpendicular to the carry-in direction); a folding part for folding a sheet; a discharge part for discharging a bent sheet from the sheet folding device; a discharge and conveyance path for conveying a sheet from the folding part to the discharge part; a discharge tray for receiving a sheet discharged; and so on. The sheet folding device employs this configuration, and is adapted to perform folding processing on each sheet or a bundle of sheets already subjected to stapling processing or the like.
Further, the sheet folding device is provided with an arm and a holding member in some cases. For example, the arm and the holding member are so provided as to project along the sheet discharge direction from the discharge part of the sheet folding device toward the discharge tray. Moreover, the holding member is typically supported in such a manner as to be rotatable upward and downward below the arm.
Here, the holding member is provided for the purpose of preventing a small-sized sheet or a small number of bent sheets from flying out of the discharge tray by being powerfully discharged. Moreover, since the sheet discharged on the discharge tray swells at its folding portion due to a sheet restoring force, the holding member has a function of pressing this swelling from above to increase the amount of sheets stacked onto the discharge tray.
On the other hand, the arm supports the holding member so that the holding member is rotatable upward and downward, and also serves a decorative function of covering the holding member.
As one example of such a device, the invention described in JP-A-2002-167120 (hereinafter referred to as Patent Document 1) is suggested. Patent document 1 describes a sheet folding device including a paper folding member, a receiving member for receiving the leading end of paper, a receiving member moving member for moving the receiving member, a pair of width shifting members, and a width adjusting member moving member for performing width adjustment on paper in the width direction and skew correction, in which the pair of width adjusting members are arranged upstream of the paper folding member on a paper carry-in path. In the invention described in Patent Document 1, a support point is provided near the sheet discharge part, and this support point permits the arm to be pivotable upward and downward and permits the holding member to be supported at the bottom surface of this arm in a manner such as to be rotatable upward and downward.
Here, referring to FIGS. 9A and 9B, a problem involved in stacking a sheet S after folding processing performed in a conventional sheet folding device 100 will be described. FIG. 9A is a sectional view illustrating a sheet S discharge direction on a discharge tray 101 in the conventional sheet folding device 100. FIG. 9B is a sectional view illustrating stack condition of sheets S on the discharge tray 101 of the conventional sheet folding device 100. The sheet folding device 100 in the description of a conventional example mainly functions to fold a bundle of sheets S. Therefore, the sheet S in FIG. 9A is normally stacked in a plural number, thereby forming a bundle of sheets S, although it is simply illustrated for avoiding complicated figure description. Other portions of the conventional sheet folding device 100 are omitted here.
As shown in FIG. 9A, the conventional sheet folding device 100 typically folds a sheet S (hereinafter, the sheet S includes a bundle of sheets S in the description of the conventional example) by a pair of folding rollers 102 forming a folding part, and then discharges it through a pair of discharge rollers 103 as a discharge part to the discharge tray 101 provided adjacently to the discharge part. Then, the conventional sheet folding device 100 is provided with an arm 104 located above the discharge tray 101 and so provided as to project in the sheet S discharge direction. This arm 104 has a support point P4 near the pair of discharge rollers 103 and is pivotable downward through some degrees. Further, below the support point P4, a support point P5 is provided, which permits a holding member 105 to be provided in such a manner as to be rotatable upward and downward.
A bent sheet S is discharged onto the discharge tray 101 with the folding portion of the sheet S oriented ahead (see FIG. 9B). Then, as shown in FIG. 9A, the discharged sheet S hits the holding member 105, and is thereby guided downward. This prevents a small-sized sheet S or a small number of bent sheets S from flying out of the discharge tray 101 and also prevents the staking on the discharge tray 101 from being disturbed. An arrow of a dashed line shows one example of the direction in which the sheet S is discharged.
Since the holding member 105 is rotatably supported, an increase in the amount of sheets S stacked onto the discharge tray 101 brings the holding member 105 up to the position indicated by a broken line of FIG. 9A (the direction of the holding member 105 is indicated by an arrow of a chain double-dashed line).
Here, stacking of a large number of bundles of sheets S onto the discharge tray 101 typically causes the folding portions of the sheets S to swell due to their restoring forces; therefore, the sheets S are laid one on another in a substantially fan-like form with the folding portions oriented outward (see FIGS. 6A and 6B). Further, the holding member 105 exerts an influence that orients the sheet S discharge direction downward, so that a sheet S newly discharged downwardly hits a sheet S previously discharged, pushing out a bundle of sheets S in the sheet S discharge direction. This consequently causes, as shown in FIG. 9B, the sheet S discharged at the most downstream portion in the sheet S discharge direction to extend over the discharge tray 101 and also causes disturbance of the stack condition of the sheets S.
As described above, the presence of the holding member 105 causes a sheet S newly discharged to hit and push out a sheet S previously discharged and at the same time be so laid as to climb a slope formed by the sheet S previously discharged. Further, as shown in FIG. 9A, the arm 104 and the holding member 105 do not move upward beyond given points, and thus continuously exert the influence that orients a discharged sheet S downward regardless of the amount of sheets S stacked. A large force for pushing out a sheet S may form, as shown in FIG. 9B, such a slope that a sheet S newly discharged can never climb. Then a sheet S discharged from the discharge part can no longer climb the slope and the sheet S covers the discharge part, resulting in a state that the sheet S can no longer be stacked onto the discharge tray 101.
As described above, when a large number of sheets are stacked onto the discharge tray, there arises a problem that the holding member provided for the purpose of increasing the stack volume on the discharge tray by controlling the swelling of discharged sheets undesirably becomes a factor that reduces the stack volume.
Thus, considering the invention described in Patent Document 1, the invention described in Patent Document 1 is intended to perform paper width adjustment and skew correction without taking a relationship between the holding member and the sheet stacking into consideration. Furthermore, Patent Document 1 provides almost no statement about the arm and the holding member, thus failing to cope with the problem described above.